1. Field of the Invention
The present invention relates to a dielectric line waveguide which forms an amplifying circuit or a modulation circuit, used in, for example, a circuit module in a millimetric wave or microwave band.
2. Description of the Related Art
Hitherto, a dielectric line waveguide has been used as a communication module in a millimetric wave band. In particular, a nonradiative dielectric line waveguide (NRD guide) is free from radiation losses and can be miniaturized due to its configuration such that a dielectric strip is inserted between two plane-parallel plates having an interval of a half-wave length or less. Thus, research is being made on applications of the NRD guides to millimetric-wave integrated circuits. An example of applications of the above type of dielectric line waveguide to an amplifying circuit is shown in HEMT Amplifier Used in NRD Guide Integrated Circuit, by Wilkinson, A. A, and Tsutomu Yoneyama, The 1990 IEICE Spring Conference, SC-2-2, (1990) pp. 2-627.
In an amplifying circuit formed by a combination of a dielectric line waveguide and a semiconductor device, as shown in the above example, the semiconductor device is conventionally disposed outside the dielectric line waveguide. Accordingly, a signal propagating in the dielectric line waveguide is first output from the waveguide and is then processed in the semiconductor device, and is once again returned to the dielectric line waveguide.
When a frequency signal (RF signal) is input into or output from a semiconductor device, impedance matching should be, in general, performed in an input/output circuit provided between a transmission line and the semiconductor device in order to improve input/output efficiency. However, the foregoing amplifying circuit in which the semiconductor device is provided on the exterior of the dielectric line waveguide encounters the following problems. Loss and distortion may be incurred in the RF signal while impedance matching is performed in the input/output circuit, such as a matching circuit, and parasitic coupling is easily generated between an external circuit, such as a semiconductor device, and the dielectric line waveguide, thereby degrading the RF characteristics. Further, the configuration of the circuit is complicated, which inevitably makes the manufacturing process very complicated as well.